This invention is concerned with constructional elements, known generally as structural cores, which replace constructional cores of the honeycomb type.
Structural cores are the subject of several U.S. Pat. Nos. such as 3,689,345, 3,813,273 and 3,642,566. These cores are in the form of open-ended polyhedrons joined together along common edges or sides. Such structural core media are generating high industrial interest because of the great strengths they possess relative to their weights. Aircraft constructional cores, for example, must possess quasi-isotropic load-carrying capabilities, including tension, compression, bending and torsional rigidity. Structural core media thus have many uses in the aircraft and other fields.
The structural core medium with which this invention is concerned is similar to that described in U.S. Pat. Nos. 3,645,833 and 3,657,059. Described in those patents is a core of interwoven fibrous filaments coated with plastic to make the core medium. The ultimate core medium is highly satisfactory. However it has the disadvantage that it is very difficult, if not heretofore impossible to produce in other than planar, sandwich or cylindrical form. Whereas an airfoil shape can be made (U.S. Pat. No. 3,645,833) it has not been possible to make polyhedrons with tetrahedral core surfaces. The jig did not exist. We have now made possible the fabrication of such polyhedrons.